1. Field of the Invention
The invention relates to microelectromechanical structures (MEMS).
2. Background
Communication systems generally require partitioning of the electromagnetic frequency spectrum. Communication transceiver devices therefore must be capable of high frequency selectivity, i.e., capable of selecting a given frequency band while rejecting all others. Frequency-selective devices, such as filters, oscillators and mixers are therefore some of the most important components within a transceiver and the quality of the devices generally dictates the overall architecture of a given transceiver.
In wireless radio frequency (RF) devices, resonators are generally used for signal filtering and generation purposes. The current state of the art typically is the use of discrete crystals to make the resonators (off-chip resonators). To miniaturize devices, MEMS resonators have been contemplated.
In a typical resonator, the resonance frequency after processing is usually different from the targeted value due to processing variation. For discrete crystals as mentioned above, such resonance frequency error is usually corrected using laser trimming technology. However, because MEMS resonators (particularly high frequency MEMS resonators) are generally much smaller in size than their crystal counterparts, traditional laser trimming technology is not a viable alternative. One alternative is to remove or add mass to the resonator beam to increase or decrease frequency. However, as beam structures are targeted to micron or submicron sizes as required for ultra-high frequency, it is generally impractical to directly modify the beam. Such modification to the beam thickness tends to be inaccurate. The inaccuracy is believed to be principally due to the sensitivity of the spring constant (k) dependency of the beam thickness. Accordingly, what is needed are techniques to modify the resonance frequency of a resonator.